U.S. patent application number 14/453431 was filed with the patent office on 2015-10-01 for method to improve surface roughness and eliminate sharp corners on an actuator layer of a mems device.
The applicant listed for this patent is InvenSense, Inc.. Invention is credited to Jong Il SHIN, Jongwoo SHIN, Peter SMEYS.
Application Number | 20150274517 14/453431 |
Document ID | / |
Family ID | 54189342 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150274517 |
Kind Code |
A1 |
SMEYS; Peter ; et
al. |
October 1, 2015 |
METHOD TO IMPROVE SURFACE ROUGHNESS AND ELIMINATE SHARP CORNERS ON
AN ACTUATOR LAYER OF A MEMS DEVICE
Abstract
A method for forming an actuator layer of a MEMS device is
disclosed. The method comprising etching the actuator layer and
annealing the actuator layer after etching to reduce surface
roughness of the MEMS device.
Inventors: |
SMEYS; Peter; (San Jose,
CA) ; SHIN; Jongwoo; (Pleasanton, CA) ; SHIN;
Jong Il; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
InvenSense, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
54189342 |
Appl. No.: |
14/453431 |
Filed: |
August 6, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14225275 |
Mar 25, 2014 |
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14453431 |
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62000418 |
May 19, 2014 |
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Current U.S.
Class: |
438/48 |
Current CPC
Class: |
B81C 1/00626 20130101;
B81C 1/00825 20130101; B81C 2201/0169 20130101 |
International
Class: |
B81C 1/00 20060101
B81C001/00 |
Claims
1. A method for forming an actuator layer of a MEMS device
comprising: etching the actuator layer; and annealing the actuator
layer after etching to reduce surface roughness of the MEMS
device.
2. The method of claim 1, wherein the annealing reduces
scallops.
3. The method of claim 1, wherein the annealing produces rounded
corners.
4. The method of claim 1, wherein the annealing comprises hydrogen
annealing.
5. The method of claim 1, wherein the annealing is performed at a
temperature greater than 1000C.
6. The method of claim 1, wherein the MEMS device comprises a MEMS
sensor.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit under 35 USC 119(e) of U.S.
Provisional Patent Application No. 62/000,418, filed on May 19,
2014, entitled "METHOD TO IMPROVE SURFACE ROUGHNESS AND ELIMINATE
SHARP CORNERS ON AN ACCELEROMETER OR GYRO ACTUATOR," and is a
continuation-in-part of U.S. patent application Ser. No.
14/225,275, filed Mar. 25, 2014, entitled "REDUCTION OF CHIPPING
DAMAGE TO MEMS STRUCTURE," (Attorney Docket No. IVS-217/5331P) all
of which are incorporated herein by reference in their
entireties.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the fabrication
of MEMS (Microelectromechanical systems) devices and more
particularly providing for rounded corners and/or minimizing
scalloping on MEMS substrates.
BACKGROUND OF THE INVENTION
[0003] MEMS devices are utilized in a variety of environments. MEMS
devices may encounter damage, such as chipping, typically induced
by mechanical shock as structures bump into one another depending
on their arrangement.
[0004] A MEMS structure is situated near a current sidewall profile
of a MEMS device. Typically chipping damage is induced by the
structures bumping with one another due to mechanical shock. It
will be appreciated by those skilled in the art that chipping
damage may occur where two structures make contact with each other
when mechanical shock is applied and can be found from an actuator
layer surface facing a second substrate. It will be further
appreciated that chipping damage may often be more problematic on
the side that is facing for example a substrate because chipped
silicon pieces may fall on to the metal electrodes on the substrate
and create the opportunity for electrical shorts between electrodes
that intended to be isolated.
[0005] Unfortunately, with ever-increasing density demands for chip
placement in circuitry, the potential for chipping damage and
electrical short situations are increasing such that increasing
dimensional placement between devices is not a viable option. What
is therefore desired is a device and method that overcomes these
challenges and provides for arranging MEMS in proximity to one
another, in densely-packed arrangements, with unique sidewall or
substrate configurations that reduce the likelihood of chipping and
electrical shorting.
SUMMARY OF THE INVENTION
[0006] The present invention fulfills these needs and has been
developed in response to the present state of the art, and in
particular, in response to the problems and needs in the art that
have not yet been fully solved by currently available
technologies.
[0007] One embodiment of the present invention provides a method
for forming an actuator layer of a MEMS device comprising etching
the actuator layer; and annealing the actuator layer after etching
to reduce surface roughness of the MEMS device.
[0008] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1A shows cross-sectional view of a MEMS device after a
deep reactive ion etch (DIRE).
[0010] FIG. 1B shows cross-sectional view of a MEMS device a high
temperature anneal.
[0011] FIG. 1C shows a close up profile of the actuator layer in
accordance with an embodiment.
DETAILED DESCRIPTION
[0012] The present invention relates generally to the fabrication
of MEMS (Microelectromechanical systems) devices and more
particularly providing for rounded corners and/or minimizing
scalloping on MEMS substrates.
[0013] The following description is presented to enable one of
ordinary skill in the art to make and use the invention and is
provided in the context of a patent application and its
requirements. Various modifications to the preferred embodiment and
the generic principles and features described herein will be
readily apparent to those skilled in the art. Thus, the present
invention is not intended to be limited to the embodiment shown but
is to be accorded the widest scope consistent with the principles
and features described herein.
[0014] In the described embodiments micro-electro-mechanical
systems (MEMS) refers to a class of structures or devices
fabricated using semiconductor-like processes and exhibiting
mechanical characteristics such as the ability to move or deform.
In the described embodiments, the MEMS device may refer to a
semiconductor device implemented as a micro-electro-mechanical
system. The MEMS structure may refer to any feature that may be
part of a larger MEMS device. MEMS devices often, but not always,
interact with electrical signals. MEMS devices include but are not
limited to gyroscopes, accelerometers, magnetometers, pressure
sensors, microphones, and radio-frequency components. Silicon
wafers containing MEMS structures are referred to as MEMS
wafers.
[0015] A structural layer may refer to the silicon layer with
moveable structures. An engineered silicon-on-insulator (ESOI)
wafer may refer to an SOI wafer with cavities beneath the silicon
structural layer. A cap wafer typically refers to a thicker
substrate used as a carrier for the thinner silicon device
substrate in a silicon-on-insulator wafer.
[0016] A MEMS substrate provides mechanical support for the MEMS
structure. The MEMS structural layer is attached to the MEMS
substrate. The MEMS substrate is also referred to as handle
substrate or handle wafer. In some embodiments, the handle
substrate serves as a cap to the MEMS structure. A cap or a cover
provides mechanical protection to the structural layer and
optionally forms a portion of the enclosure. Standoff defines the
vertical clearance between the structural layer and the IC
substrate.
[0017] Standoff may also provide electrical contact between the
structural layer and the IC substrate. Standoff may also provide a
seal that defines an enclosure. Integrated Circuit (IC) substrate
may refer to a silicon substrate with electrical circuits,
typically CMOS circuits. A cavity may refer to a recess in a
substrate. Chip includes at least one substrate typically formed
from a semiconductor material. A single chip may be formed from
multiple substrates, where the substrates are mechanically bonded
together. Multiple chip includes at least 2 substrates, wherein the
2 substrates are electrically connected, but do not require
mechanical bonding.
[0018] An actuator layer etch process of a MEMS device comprises
cycles of etch and sidewall passivation. Owing to this cyclic etch
and passivation process, the sidewall tends to have peaks and
valleys or so called `scallops`. If there are sharp peaks at the
scallop, in-plane movement of an actuator layer can cause small
particles due to the impact of two adjacent MEMS surfaces.
[0019] One of the challenges in a MEMS device is breakage induced
by in-plane and/or out-of plane movement of the actuator layer.
In-plane movement of the actuator layer causes friction between two
surfaces and therefore may result in scallops. Furthermore, out of
plane movement of the actuator layer at a tilted angle can lead to
relatively larger chipping along sharp corners of the actuator
layer. Having a MEMS directly integrated onto CMOS substrate, the
chipping and/or particles can result in CMOS circuit short leading
to device failure(s).
[0020] Applicants have addressed the issue of scallops and sharp
corners in U.S. patent application Ser. No. 14/225,275, filed Mar.
25, 2014, entitled "REDUCTION OF CHIPPING DAMAGE TO MEMS
STRUCTURE," (Attorney Docket No. IVS-217/5331P) assigned to the
assignee of the present application which is incorporated by
reference in the present specification. Although the techniques
disclosed in the above identified application are effective,
different and improved methods to address the problem of scallops
and sharp corners on the surface of the actuator layer are
desired.
[0021] In a method in accordance with an embodiment, a surface of a
MEMS device is annealed at high temperature in hydrogen ambient
which increases silicon atom ion mobility on the surface.
Advantages of applying a high temperature anneal are removal of
scallops and sharp corners on the surface of the MEMS device. A
method in accordance with an embodiment reduces particles on the
surface generated by in-plane friction and reduces chipping that
occurs during out of plane movement of the actuator layer due to
the rounded corners thereon. To describe the features of the
present invention in more detail refer now to the following
description in conjunction with the accompanying Figures.
[0022] FIG. 1A shows cross-sectional view of a MEMS device 200
after a first deep reactive ion etch (DRE). The MEMS device 200
comprises a MEMS substrate 203 coupled to a MEMS handle wafer 202.
In this embodiment the handle wafer includes an oxide layer 201 on
a top surface thereof. The MEMS device 200 also includes an upper
cavity 207 and a MEMS bond anchor or standoff 206. The MEMS
substrate 203 also includes an actuator layer 205 which is
patterned by the DRE as shown in FIG. 1B.
[0023] A subsequent high temperature anneal will provide smooth
surfaces and rounded corners for the actuator layer 205. What is
meant by a high temperature anneal in the context of a hydrogen
environment is a temperature of 1000 degrees C. or greater. What is
meant by rounded corners are corners with a radius of curvature
that is greater than or equal to 0.2 um.
[0024] FIG. 1C shows a close up profile of the actuator layer 205
in accordance with an embodiment. As shown FIG. 1C, scallops are
minimized and rounded corners are provided against a CMOS surface
300 based upon the above identified process. Accordingly, by
applying a high temperature anneal scallops and sharp corners on
the surface of the MEMS device are substantially reduced.
[0025] In the described embodiments, the device can be any MEMS
device or sensor with a moveable structure such as but not limited
to accelerometer, gyroscope, magnetic sensors and resonators. In
the described embodiments, the IC substrate can include electronic
circuits for sensing and processing the motion of the MEMS device,
without limitation. One skilled in the art would appreciate that
the IC substrate 920 can be substituted with any type of substrate
such as a ceramic substrate or a silicon substrate.
[0026] Any theory, mechanism of operation, proof, or finding stated
herein is meant to further enhance understanding of the present
invention and is not intended to make the present invention in any
way dependent upon such theory, mechanism of operation, proof, or
finding. It should be understood that while the use of the words
preferable, preferably, or preferred in the description above
indicates that the feature so described may be more desirable, it
nonetheless may not be necessary and embodiments lacking the same
may be contemplated as within the scope of the invention, that
scope being defined by the claims that follow.
[0027] Although the present invention has been described in
accordance with the embodiments shown, one of ordinary skill in the
art will readily recognize that there could be variations to the
embodiments and those variations would be within the spirit and
scope of the present invention, such as the inclusion of circuits,
electronic devices, control systems, and other electronic and
processing equipment. Accordingly, many modifications may be made
by one of ordinary skill in the art without departing from the
spirit and scope of the appended claims. Many other embodiments of
the present invention are also envisioned.
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